The present invention relates to the field of containers. More particularly, the present invention relates to stackable cardboard containers with stacking guides that are self-aligning.
Three general types of stackable cardboard boxes with interlocking and stack stabilizing features, primarily used for the packaging and transportation of perishables such as fruits and vegetables, are known in the art. The first type has tabs, extended from a side or end wall, that fit into a corresponding slot or pocket. Examples may be found in U.S. Pat. No. 5,452,848 issued to Mur Gimeno and U.S. Pat. No. 3,940,053 issued to Putman and Wytko. A second type of box maintains stability in a stack by resting each corner of an upper box into the extended corner catches of a lower box. Examples are found in U.S. Pat. No. 4,053,098 issued to Baptist and U.S. Pat. No. 5,549,242 issued to Gimeno.
A third type of stack stabilizing solution is described in U.S. Pat. No. 5,487,505 issued to Nilsson, in which a foldable carton has a partially lowered sidewall to increase airflow around packed produce. The carton is constructed by inserting a group of flaps into corresponding slots, which both hold the box together and provide a diagonal corner support. Tabs extend from each corner support of a lower carton and fit into corresponding slots in the bottom of an upper carton. To mate boxes with the Nilsson tab and slot system, the operator must first accurately align and insert a tab into the appropriate slot.
While these known types of stack stabilizing systems can maintain alignment of a stack of boxes, they do not completely address certain stacking problems. They generally require a relatively high degree of precision to accurately align the tabs and slots. A slight misalignment between a tab and slot often results in the tab being folded over or crushed and therefore rendered ineffective. The tab solutions may also fail to compensate for the destabilizing effect of a worn tab. A worn tab, which is precisely aligned in a slot may nonetheless be able to xe2x80x9cdriftxe2x80x9d longitudinally within the slot, thereby allowing the stack to be moved out of plumb.
Accordingly, a container in which the tabs of a lower box both capture the misaligned apertures of a similar upper box and guide the upper box into alignment would be desirable. Additionally, a stack-stabilizing system which reduces the xe2x80x9cdriftxe2x80x9d of a properly inserted worn tab, thereby causing a stack of boxes, even one with worn or damaged tabs, to remain in plumb, would also be desirable.
It is an object of this invention to provide an improved box or container which, by virtue of its interlocking tabs and apertures, can compensate for stacking misalignments and urge boxes into proper alignment during stacking. Once stacked, the movement of an interlocking tab within an aperture is further inhibited by a tab guide or recess surrounding the interlocking tab. Such a box can be constructed by scoring and folding a single sheet of material known as a xe2x80x9cblankxe2x80x9d. To strengthen the corners of the box and resist collapsing during stacking, a corner panel extends from sidewall to end wall diagonally across each of the corners. Each corner panel can also support an upwardly projecting interlocking tab. To provide even more vertical or stacking support, particularly in the corner areas, multiple blanks can be used as in a bliss-type container.
Each tab is shaped to form a narrow head generally tapering outwardly toward a wide base. Apertures, of a dimension equal to the wide base of each tab, and therefore xe2x80x9coversizedxe2x80x9d relative to the narrow head, are formed in the bottom of the box. The aperture can advantageously be round. The self-alignment feature is derived from the interaction of the generally tapered tabs and relatively xe2x80x9coversizedxe2x80x9d apertures which serve the following dual functions: (1) tab placement, the xe2x80x9coversizedxe2x80x9d apertures can accept a misaligned tab head, thereby facilitating tab placement within the apertures without as high a degree of stacking precision; and (2) self-alignment, the tab widens from head to base as it fills the aperture thereby tending to cause alignment of the tabs within the apertures.
When stacking boxes which have this self-alignment system, because the tabs are positioned above the bottom panel and remote from the outer walls of the box, the apertures formed in the bottom panel are able to catch the tab""s narrow head, although it may be misaligned in any direction with respect to the center of the aperture. Then, once a tab""s narrow head is within the vicinity of an aperture and the upper box is lowered, the apertures of the upper box are filled with the girth of the tab""s wide base thereby urging the upper box into alignment with the lower box.
In previously known boxes with slot and tab arrangements, a slight misalignment of the tab and slot will often result in the tab being bent or crushed. In the case of boxes with reinforced tabs, misalignment results in the boxes stacking unevenly with protruding tabs, preventing a positive interlock of box bottoms and tops.
The integrity of a stack of boxes constructed according to the invention may be further enhanced by causing the tabs of a lower box to be inserted into corresponding tab recesses of an upper box. Another advantage over other tab recess is that alignment of the stacked boxes is maintained by the circumference of the tab against the outline of the recess. This recess is more effective at maintaining a positive lock on a damaged tab than prior art slots which will allow a tab with edge damage near its base to xe2x80x9cdriftxe2x80x9d. Tab xe2x80x9cdriftxe2x80x9d is the side to side movement of a tab within a slot resulting when a tab""s worn edge, near its base, allows the fully inserted tab to move. A drifting tab will allow a stack of boxes to move out of plumb and thereby destabilizes the entire stack.
Another noteworthy feature of this invention is that crush strength and load-bearing capacity of the box has been increased by forming a region of double thick wall near each end of each sidewall thereby minimizing the length of the region of single thickness sidewall.